Thermomechanical process for producing a planar resist structure

ABSTRACT

In a thermomechanical process for planarizing a resist layer applied to a partly elevated carrier area, a resist structure, in particular an encapsulation for electronic components, is obtained. In this case, a dry resist sheet, formed of a composite of a temperature-resistant protective sheet and a photosensitive layer, is applied by its photosensitive layer to a surface of the carrier and the dry resist sheet is planarized under pressure and with heat. After which the photosensitive layer is exposed, and the protective sheet is removed and the photosensitive layer is developed.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a divisional application of U.S. application Ser. No.09/707,029, filed Nov. 6, 2002, which was a continuation ofInternational Application PCT/DE99/01352, filed May 5, 1999, whichdesignated the United States, and which was not published in English.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to a thermomechanical process forplanarizing a photo-patternable layer applied to a partly elevatedcarrier area.

[0004] The Patent Cooperation Treaty (PCT) application with theinternational publication number WO 95/30276 discloses anencapsulation—which the applicant designates as PROTEC—for electroniccomponents, in particular for components operating with surface acousticwaves—SAW components. The encapsulation has, in regions of the componentstructures, e.g. in regions of interdigital transducers and ofoptionally required acoustic attenuation masses that are usually appliedusing screen printing technology, recesses which accommodate thecomponents. In one of its exemplary embodiments, the above-mentioned PCTapplication provides for this purpose a frame-like carrier applied tothe component substrate, e.g. a piezo-electric substrate, and optionallysupports on which a covering layer is disposed. In this case, thecarrier, the supports and the covering layer may be formed by a sheetwhich, on the side of the component substrate, contains depressionsspanning the component structures and is applied to the componentsubstrate e.g. by adhesive bonding, welding or lamination.

[0005] In accordance with a further known proposal according to the PCTapplication, a photo-patternable material, i.e. a so-called dry resistsheet, is used for the carrier and optionally the supports. By way ofexample, this may be a photoresist or a material which can be patternedby UV light, and which is exposed in such a way that, after it has beendeveloped, only the active components, in particular filter structures,the acoustic attenuation mass and the areas provided for makingelectrical contact with these component structures are uncovered. Asecond layer, namely a covering layer, is then applied to the carrierthus produced and—if present—the supports, which layer likewise containsa dry resist sheet, i.e. a photo-patternable material of theabove-mentioned type, which is likewise exposed and developed after ithas been applied. This material ultimately forms the recesses givensufficient thickness of the first layer containing carrier andoptionally supports, together with the layer.

[0006] This type of encapsulation—also called PROTEC—which ultimatelycontains a successive application of two layers of dry resist sheets,the application in each case being correspondingly treated byphototechnology, is unsuitable for all cases in which the dry resistsheets are intended to bear directly on the acoustic attenuation mass.

[0007] This is because, in the case of standard lamination, the appliedfirst layer or first dry resist sheet and, consequently, also the secondlayer or second dry resist sheet follow the uneven contour profile ofthe acoustic attenuation mass. The uneven application of the second dryresist sheet to the already unevenly bearing first dry resist sheet isunacceptable, however, since under the technically expedient laminationconditions for the second layer, the resulting encapsulations, such ase.g. coverings for chips of SAW components, are not tight.

SUMMARY OF THE INVENTION

[0008] It is accordingly an object of the invention to provide athermomechanical process for producing a planar resist structure, whichovercomes the above-mentioned disadvantages of the prior art devices andmethods of this general type, which ensures reliable application of thesecond layer or dry resist sheet and thus a hermetically tightencapsulation of chips of electronic components, in particular of SAWcomponents.

[0009] With the foregoing and other objects in view there is provided,in accordance with the invention, an electronic component. Theelectronic component is formed of a substrate, elevated structuresdisposed on the substrate, and a resist structure having surfacesapplied above the elevated structures. The resist structure bearstightly on the substrate and the elevated structures. The resiststructure has a varying layer thickness such that the surfaces of theresist structure lie substantially in one plane.

[0010] Only the planar resist structure according to the inventionenables a further layer to be applied conformally in such a way that agood connection to the resist structure, reliable bearing on the latterand, consequently, a tight encapsulation can be produced.

[0011] Assuming that the protective sheet which forms the dry resistsheet in a composite with a photosensitive layer, is atemperature-resistant sheet, i.e. a sheet which cannot be destroyed evenat relatively high temperatures, then the solution provided by theprocess according to the invention is that the dry resist sheet isapplied by its photosensitive layer to the surface of the carrier. Thedry resist sheet is then treated under pressure and with heat in such away that the photosensitive layer is planarized. The photosensitivelayer is then exposed, and the protective sheet is removed and thephotosensitive layer is developed.

[0012] If a non-temperature-resistant protective sheet is used, then theinvention provides for the protective sheet, after the application ofthe dry resist sheet, to be drawn off from the photosensitive layer andreplaced by a temperature-resistant separating sheet. Thetemperature-resistant separating sheet has a non-adhering layer on itssurface directed toward the photosensitive layer. The separating sheettogether with the photosensitive layer is treated under pressure andwith heat in such a way that the photosensitive layer is planarized. Theseparating sheet is then removed and the photosensitive layer is exposedand developed.

[0013] The application or the lamination of the dry resist sheet for thefirst layer is done in accordance with the customary standard processesand leads to a layer free from air bubbles which follows the topographyof the attenuation mass applied using screen printing technology, forexample. It is only by virtue of the planarization, in which, in thecase of a temperature-resistant protective sheet, the dry resist sheettogether with the carrier and, in the case of anon-temperature-resistant protective sheet, the carrier coated with thephotosensitive layer, together with the separating sheets, are disposedbetween hot plates and compressed. The viscosity of the photosensitivematerial of the first layer decreases, on account of the temperatureincrease, to such an extent that, as a result of the pressure exertedaxially on the carrier, the material of this layer flows from the zonessituated above the screen printing into the zones without theattenuation mass.

[0014] Consequently, the photosensitive layer of the first layer isleveled to such an extent that, after subsequent photo-patterning, thesecond layer of dry resist sheet can be laminated on in a manner knownper se and the resulting encapsulations, e.g. of chips of electroniccomponents, are hermetically tight.

[0015] The material is prevented from sticking to the hot plates orpressing apparatus by virtue of the adequate temperature resistance(present in any case) of the protective sheet, e.g. a polyester sheet.

[0016] In accordance with an added feature of the invention, a resistlayer having a uniform layer thickness is provided that covers theresist structure.

[0017] In accordance with an additional feature of the invention, theresist structure forms a frame, and the resist layer forms a covermatching the frame. The frame and the cover together form a cap-shapedcovering and enclose a cavity between the substrate, the frame and thecover.

[0018] In accordance with another feature of the invention, the resiststructure and the resist layer are formed from a dry resist sheet.

[0019] In accordance with a further feature of the invention, theelevated structures have metalization layers and/or interconnectstructures.

[0020] With the foregoing and other objects in view there is furtherprovided, in accordance with the invention, a thermomechanical processfor producing a planar resist structure. The process includes the stepsof:

[0021] a) providing a carrier having a surface and elevations disposedon the surface;

[0022] b) applying a dry resist sheet formed of a composite of atemperature-resistant protective sheet and a photosensitive layer to thesurface of the carrier such that the photosensitive layer is applied tothe surface of the carrier;

[0023] c) subjecting the dry resist sheet to pressure and heat resultingin the photosensitive layer being planarized;

[0024] e) exposing the photosensitive layer;

[0025] f) removing the temperature-resistant protective sheet; and

[0026] g) developing the photosensitive layer resulting in a developedphotosensitive layer.

[0027] In accordance with an added feature of the invention, there isthe step of providing electronic components as the elevations formed onthe carrier.

[0028] In accordance with an additional feature of the invention, thereare the steps of:

[0029] a) applying a photosensitive layer side of a further dry resistsheet, formed of a composite having a protective sheet and thephotosensitive layer, to the developed photosensitive layer;

[0030] b) exposing the photosensitive layer of the further dry resistsheet;

[0031] c) removing the protective sheet of the further dry resist sheet;and

[0032] d) developing the photosensitive layer of the further dry resistsheet resulting in a further developed photosensitive layer.

[0033] In accordance with another feature of the invention, there arethe steps of: applying a photosensitive layer side of a further dryresist sheet, formed of a composite of a protective sheet and thephotosensitive layer, to the developed photosensitive layer; drawing offthe protective sheet of the further dry resist sheet; and exposing anddeveloping the photosensitive layer of the second dry resist sheetresulting in a further developed photosensitive layer.

[0034] In accordance with a further feature of the invention, there isthe step of curing the developed photosensitive layer and the furtherdeveloped photosensitive layer.

[0035] In accordance with a further added feature of the invention,there are the steps of disposing and compressing the dry resist sheettogether with the carrier between hot plates.

[0036] In accordance with a further additional feature of the invention,there is the step of using a polyester sheet as thetemperature-resistant protective sheet.

[0037] With the foregoing and other objects in view there is furtherprovided, in accordance with the invention, a thermomechanical processfor producing a planar resist structure. The process includes the stepsof:

[0038] a) providing a carrier having a surface and elevations disposedon the surface;

[0039] b) applying a dry resist sheet formed of a composite of anon-temperature-resistant protective sheet and a photosensitive layer tothe surface of the carrier such that the photosensitive layer is appliedto the surface of the carrier;

[0040] c) separating and removing the non-temperature-resistantprotective sheet from the photosensitive layer;

[0041] d) applying a temperature-resistant separating sheet having anon-adhering layer on the photosensitive layer such that thenon-adhering layer resides on the photosensitive layer;

[0042] e) subjecting the temperature-resistant separating sheet togetherwith the photosensitive layer to pressure and heat such that thephotosensitive layer is planarized;

[0043] f) removing the temperature-resistant separating sheet;

[0044] g) exposing the photosensitive layer; and

[0045] h) developing the photosensitive layer.

[0046] In accordance with an added feature of the invention, there arethe steps of disposing and compressing the carrier coated with thephotosensitive layer together with the temperature-resistant separatingsheet, between hot plates.

[0047] In accordance with another feature of the invention, there is thestep of using a polyolefin sheet as the non-temperature-resistantprotective sheet.

[0048] In accordance with an additional feature of the invention, thereis the step of forming the non-adhering layer of thetemperature-resistance separating sheet from silicone.

[0049] In accordance with a concomitant feature of the invention, thereis the step of forming the non-adhering layer of thetemperature-resistance separating sheet from polytetrafluoroethylene(PTFE).

[0050] Other features which are considered as characteristic for theinvention are set forth in the appended claims.

[0051] Although the invention is illustrated and described herein asembodied in a thermomechanical process for producing a planar resiststructure, it is nevertheless not intended to be limited to the detailsshown, since various modifications and structural changes may be madetherein without departing from the spirit of the invention and withinthe scope and range of equivalents of the claims.

[0052] The construction and method of operation of the invention,however, together with additional objects and advantages thereof will bebest understood from the following description of specific embodimentswhen read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] FIGS. 1 to 5 are diagrammatic, sectional views, showing essentialmethod steps for producing a first exemplary embodiment of the subjectmatter according to the invention; and

[0054] FIGS. 6 to 9 are sectional views of essential method steps forproducing a second exemplary embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] In all the figures of the drawing, sub-features and integralparts that correspond to one another bear the same reference symbol ineach case. Referring now to the figures of the drawing in detail andfirst, particularly, to FIGS. 1-3 thereof, there is shown the productionof a first exemplary embodiment of a surface acoustic wave (SAW)component. The SAW component is formed from a dry resist sheet 2laminated in a customary manner onto one surface 6 of a carrier 1 madeof a piezo-electric material. In the case of customary mass production,the carrier 1 is a wafer, which has, in regions of its individual SAWcomponents, acoustic attenuation masses 5 in each case applied usingscreen printing technology, for example. The dry resist sheet 2 isformed of a composite of a temperature-resistant protective sheet 3,e.g. a polyester sheet, and a photosensitive layer 4.

[0056] In a further step—see FIG. 2—the wafer thus coated is disposedbetween heating plates 7, 8 of a pressure apparatus and the dry resistsheet 2 is planarized—see FIG. 3—under pressure—see arrows F. Due to theheat, the photosensitive material 4, as viewed in arrow direction A(FIG. 2), partly flows into the zones that are free of the attenuationmasses 5.

[0057] Afterwards, the photosensitive layer 4 is exposed, the protectivesheet 3 is drawn off and the exposed photosensitive layer 4 isdeveloped, thereby concluding the production process for the firstPROTEC layer, see FIG. 4.

[0058] The starting product that is used for producing the second PROTEClayer, required for creating the complete encapsulation, is once again adry resist sheet 2′ of the constitution mentioned above, which isapplied by its photosensitive layer 4′ to the developed planar layer 4in a manner known per se, see FIG. 5. After which the photosensitivelayer 4′ is exposed, a protective sheet 3′ is removed and the exposedphotosensitive layer 4′ is developed.

[0059] Alternatively, instead of the above-mentioned dry resist sheet 2′for the second PROTEC layer with the temperature-resistant protectivesheet 4′, it is possible to apply to the developed layer 4 a dry resistsheet which has a non-temperature-resistant protective sheet, e.g.polyolefin sheet. In this case, with insufficient transmission for thewavelengths used, the photosensitive layer can only be exposed after theprotective sheet has been removed.

[0060] For the final encapsulation, after the application anddevelopment of the second photosensitive layer, the developed layers arecured e.g. by UV radiation and/or thermally.

[0061] In the method in accordance with the exemplary embodimentaccording to FIGS. 6 to 9, use is made of a dry resist sheet 12 for thefirst PROTEC layer which contains a composite of anon-temperature-resistant protective sheet 13, e.g. a polyolefin sheet,with a photosensitive layer 14—see FIG. 6. On account of itsinsufficient heat resistance, the protective sheet must be removedbefore the planarization (already explained)—see FIG. 7—and replaced bya temperature-resistant separating sheet 15, e.g. a polyester sheet. Onits surface directed toward the carrier 1, the separating sheet 15 hase.g. a silicone layer or a polytetrafluoroethylene layer (PTFE layer)17, which, during the subsequent planarization, see FIGS. 8-9, preventsthe photosensitive layer 14 from sticking to the heating plate 7 andenables the later removal of the separating sheet 15 from thephotosensitive layer 14.

[0062] After planarization has been carried out, then—as has alreadybeen described with reference to the first exemplary embodiments—theseparating sheet 15 is removed and then the photosensitive layer 14 isexposed and developed, thereby creating the first PROTEC layer of theencapsulation.

[0063] Depending on the sheet used, the second PROTEC layer is onceagain produced in one of the ways that have already been described forthe first exemplary embodiment, which results in that it is notnecessary to explain these production steps again.

1. A thermomechanical process for producing a planar resist structure,which comprises the steps of: providing a carrier having a surface andelevations disposed on the surface; applying a dry resist sheet formedof a composite of a temperature-resistant protective sheet and aphotosensitive layer to the surface of the carrier such that thephotosensitive layer is applied to the surface of the carrier;subjecting the dry resist sheet to pressure and heat resulting in thephotosensitive layer being planarized; exposing the photosensitivelayer; removing the temperature-resistant protective sheet; anddeveloping the photosensitive layer resulting in a developedphotosensitive layer.
 2. The process according to claim 1, whichcomprises providing electronic components as the elevations formed onthe carrier.
 3. The process according to claim 1, which comprises:applying a photosensitive layer side of a further dry resist sheet,formed of a composite having a protective sheet and the photosensitivelayer, to the developed photosensitive layer; exposing thephotosensitive layer of the further dry resist sheet; removing theprotective sheet of the further dry resist sheet; and developing thephotosensitive layer of the further dry resist sheet resulting in afurther developed photosensitive layer.
 4. The process according toclaim 1, which comprises applying a photosensitive layer side of afurther dry resist sheet, formed of a composite of a protective sheetand the photosensitive layer, to the developed photosensitive layer;drawing off the protective sheet of the further dry resist sheet; andexposing and developing the photosensitive layer of the second dryresist sheet resulting in a further developed photosensitive layer. 5.The process according to claim 4, which comprises curing the developedphotosensitive layer and the further developed photosensitive layer. 6.The process according to claim 1, which comprises disposing andcompressing the dry resist sheet together with the carrier between hotplates.
 7. The process according to claim 1, which comprises using apolyester sheet as the temperature-resistant protective sheet.
 8. Athermomechanical process for producing a surface acoustic wavecomponent, which comprises the steps of: providing a wafer having asurface and elevations disposed on the surface; applying a dry resistsheet formed of a composite of a temperature-resistant protective sheetand a photosensitive layer to the surface of the wafer such that thephotosensitive layer is applied to the surface of the wafer; subjectingthe dry resist sheet to pressure and heat resulting in thephotosensitive layer being planarized; exposing the photosensitivelayer; removing the temperature-resistant protective sheet; anddeveloping the photosensitive layer resulting in a developedphotosensitive layer.
 9. A thermomechanical process for producing aplanar resist structure, which comprises the steps of: providing acarrier having a surface and elevations disposed on the surface;applying a dry resist sheet formed of a composite of anon-temperature-resistant protective sheet and a photosensitive layer tothe surface of the carrier such that the photosensitive layer is appliedto the surface of the carrier; separating and removing thenon-temperature-resistant protective sheet from the photosensitivelayer; applying a temperature-resistant separating sheet having anon-adhering layer on the photosensitive layer such that thenon-adhering layer resides on the photosensitive layer; subjecting thetemperature-resistant separating sheet together with the photosensitivelayer to pressure and heat such that the photosensitive layer isplanarized; removing the temperature-resistant separating sheet;exposing the photosensitive layer; and developing the photosensitivelayer.
 10. The process according to claim 9, which comprises disposingand compressing the carrier coated with the photosensitive layertogether with the temperature-resistant separating sheet, between hotplates.
 11. The process according to claim 9, which comprises using apolyolefin sheet as the non-temperature-resistant protective sheet. 12.The process according to claim 9, which comprises forming thenon-adhering layer of the temperature-resistance separating sheet fromsilicone.
 13. The process according to claim 9, which comprises formingthe non-adhering layer of the temperature-resistance separating sheetfrom polytetrafluoroethylene (PTFE).